1. Field of the Invention
The present invention relates to an optical element used in a backlight unit for a liquid crystal display and, more particularly, to an optical element capable of increasing an angular field while improving luminance by condensing light, and a backlight unit and a liquid crystal display including the same.
2. Description of the Related Art
As is well known in the art, a liquid crystal display (LCD) is widely used as an image display means of various devices such as a personal computer (e.g., a notebook and a desktop computer) and TV. The LCD is rapidly improving its features every year in order to meet user requests.
The liquid crystal panel of an LCD requires a backlight unit since it does not spontaneously emit light on its own. The backlight unit is composed of a variety of optical components, and in particular, includes an optical element for improving luminance.
In the accompanying drawings, FIG. 1 is a schematic configuration view illustrating a conventional LCD. The LCD includes a backlight unit 1 and a liquid crystal panel 2. The backlight unit 1 includes a light source 10, a light guide plate 12, a diffuser sheet 13, and a prism sheet 14. With this configuration, light emitted from the light source is diffused across a wide area through the light guide plate 12, is converted into a surface light source with a more-uniform brightness through the diffuser sheet 13, and is then condensed to a higher luminance through the prism sheet 14.
The optical element used in the above-described LCD has undergone technical development aimed improving a light-condensing function for the purpose of high luminance. This is because the LCD is mainly used in personal electronics such as a mobile communication device and a notebook computer, in which an angular field is relatively less important.
Recently, the importance of achieving a wider angular field continues to increase. For example, an LCD TV requires a wider angular field so that several people in various positions can watch at the same time. A navigator of a vehicle also requires a wider angular field so that both the driver and the passenger in the seat next to the driver can watch the screen at the same time.
Conventional methods for satisfying the above-mentioned requirements of improving luminance and enlarging an angular field include a method of layering a plurality of diffuser sheets one on another and a method of diffracting and diffusing light by inserting nano-particle beads into the top edge of a prism.
However, luminance is lowered if three or more diffuser sheets are layered one on another. This is an obstacle in the way of designing a thin product. In addition, the inserted beads are expensive and thus reduce economic competitiveness due to an increase in cost.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgment or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.